Which U.S. stock index lost 22.6% in the single trading day called Black Monday in 1987?

The Dow Jones Industrial Average lost 22.6% on October 19, 1987, the U.S. stock-market crash called Black Monday.

That fall was the largest one-day percentage decline in the Dow's history. Selling spread rapidly across international markets, making Black Monday a global crash rather than an isolated New York event.

Program trading, portfolio insurance, overvalued shares, rising interest rates, and international trade tensions all contributed to the turmoil. The exact combination of causes remains debated, but modern computerized trading clearly accelerated the sell-off.

The S&P 500 and Nasdaq also fell sharply that day, but neither was the index associated with the famous 22.6% figure. The Dow later recovered its pre-crash closing level.